mm: shmem: use new radix tree iterator

In shmem_find_get_pages_and_swap(), use the faster radix tree iterator
construct from commit 78c1d784 ("radix-tree: introduce bit-optimized
iterator").
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

@@ -335,19 +335,19 @@ static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
 					pgoff_t start, unsigned int nr_pages,
 					struct page **pages, pgoff_t *indices)
 {
-	unsigned int i;
-	unsigned int ret;
-	unsigned int nr_found;
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_pages)
+		return 0;
 
 	rcu_read_lock();
 restart:
-	nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
-				(void ***)pages, indices, start, nr_pages);
-	ret = 0;
-	for (i = 0; i < nr_found; i++) {
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
 		struct page *page;
 repeat:
-		page = radix_tree_deref_slot((void **)pages[i]);
+		page = radix_tree_deref_slot(slot);
 		if (unlikely(!page))
 			continue;
 		if (radix_tree_exception(page)) {
@@ -364,17 +364,16 @@ static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
 			goto repeat;
 
 		/* Has the page moved? */
-		if (unlikely(page != *((void **)pages[i]))) {
+		if (unlikely(page != *slot)) {
 			page_cache_release(page);
 			goto repeat;
 		}
 export:
-		indices[ret] = indices[i];
+		indices[ret] = iter.index;
 		pages[ret] = page;
-		ret++;
+		if (++ret == nr_pages)
+			break;
 	}
-	if (unlikely(!ret && nr_found))
-		goto restart;
 	rcu_read_unlock();
 	return ret;
 }